In a conventional vehicle, longitudinally running beams, called side rails, form part of the vehicle's body, and, among other things, support a front bumper. The beams are typically tubular shaped and are generally designed to absorb frontal impact loads exerted against the front bumper in the longitudinal direction of the vehicle. In order to absorb the energy of these frontal loads, the beams are designed to axially crush. To provide for a more controlled crush of these beams, triggers are sometimes incorporated into the beams. They are generally located along the sides of the beams.
A typical crush triggering type of configuration incorporates symmetrical beads, whether located as side beads or beads located on the corners of a beam, such as corner divots. By allowing the beads to initiate crush in the tubular structure of these beams, a lower overall crush load and/or a somewhat more predictable crush deformation will take place. Properly designed beads can also result in a somewhat lower variation between peak and minimum loadings of the beam. These types of beads are in use, but due to the symmetry that most of them possesses, they do not predispose the structure to crush in a consistent manner, with consistent loadings.
Consistency of crush for these beams is desired because it has the advantage of improved predictability from vehicle-to-vehicle, allowing for more precision in the design. Also, by knowing beforehand which way a structure will consistently buckle, components mounted near the frame rails of a vehicle can be positioned in the structure so that they do not interfere with the beams during crushing,
In an attempt to overcome these shortcomings of typical symmetrical triggers, asymmetrical triggers can be used to better control deformation of the beam structure. This forces the deformation during crush to move more consistently in a desired mode. Further, asymmetrical triggers generally will have a lower overall energy absorption and less variation of force over time than symmetric triggers. This results in a desirable characteristic of less load fluctuation. A reduction in load fluctuation assures that the structure supporting the frame rails will not collapse prematurely while the frame rails are crushing, which further leads to greater predictability in load characteristics.
U.S. Pat. No. 4,702,515 to Karo et al. discloses a structure that uses asymmetrical beads on the sides of a beam in an attempt to better predict and control the crush deformation characteristics by proper longitudinal spacing of the beads along the beam. It discloses alternating side beads inward and outward to control the beam crush deformation. It also discloses substituting some of the side beads with corner beads to co-operate with the side beads to control the crush deformation at the given longitudinal spacing. However, Karo et al. does not disclose being able to control the crush completely with corner beads, nor how this could be properly used in an asymmetrical fashion to adequately control all of the crush characteristics.
The corners of the beams absorb much more of the energy than the sides. Thus, to better control and provide for more consistent loading, the crush of the corners of the beams must be adequately controlled. Consequently, asymmetrical corner beads are better than side beads for controlling loading, particularly in heavy gauge sections, such as frames in light and heavy duty trucks and large automobiles, when a lowering of the axial crush load is desired. This is important since heavy gage frames are thick and, as a result, can cause the crush force to be too high for good overall crush characteristics of that beam.
One consequence, when employing corner beads, is the fact that when corner beads are employed solely to reduce the frontal crush loads required in heavy gage beams, the bending moment of inertia of the beam is reduced at the cross-sections where the beads are. This can sometimes be undesirable, particularly farther back on the beam where beam bending will be greater. This is not the case with side beads, which will slightly increase the bending moment of inertia. Thus, a further desire exists to allow for controlled crush employing corner beads while minimizing the reduction in bending capability of the beam.